I ran FreshDiagnose on a computer, and I can't tell if it supports 64-bit instructions. It says the data bus width is 64-bit, but I'm not sure what that means. Here is the output.

Code:
Processor
This module contains information about your computer's central processor(s) and its capabilities.


                                          
Processor                                 
Model                                     Intel Pentium 4
Type                                      Primary Processor
Vendor                                    Intel Corporation
Family                                    Intel P4 Family
Hardcoded Name                            Intel(R) Xeon(TM) CPU 3.00GHz
Frequency                                 2992 MHz
Family/Model/Stepping                     15/4/3
Logical CPU Count                         2
Apic ID                                   6
CL Flush                                  8
                                          
Detailed Info                             
Address Bus Width                         36 Bit
Core Details                              126 µOPs, 48 Loads, 24 Stores In-Flight
Data Bus Width                            64 Bit
Execution Speed                           Up to 6 µOPs/Cycle
Execution Units                           Double-pumped ALU, FP Move/Store/FXCH, Double-pumped ALU,
                                          Slow ALU, FP Execute, Load, Store
Floating Point                            Integrated
Instruction Decoder                       1x IA-32/Cycle
Instruction Set                           IA-32
Multimedia                                MMX, SSE, SSE2
Multiprocessing                           SMP, using integrated local xAPICs
Physical Memory                           2^36 Bit (64 GB)
Pipeline Depth                            20 Stages
Power Management                          HLT, STPCLK, SMI/SMM, Sleep, Deep Sleep,
                                          Automatic Clock Throttling
Processor Core                            RISC, Out-of-order and Speculative Execution
Processor Modes                           Real, Protected, Virtual, Paging, SMM, Probe Mode
Registers                                 32 Bit Integer, 80 Bit FP, 64 Bit MM, 128 Bit SSE and SSE2
Split Voltage                             Yes (Automatically determined via VID Pins)
Supported External Bus Speed              100, 133 MHz Quad-Pumped, AGTL+
Supported Multiplier                      13.0x, 14.0x, ..., 24.0x
Virtual Memory                            65,528 GB (~64 TB)
                                          
Cache Configuration                       
L1 Code TLB                               4 KB pages, 4-way set associative, 32 entries
                                          4 KB/4 MB/2 MB pages, fully associative, 64 entries
L1 Data TLB                               4 KB/4 MB pages, fully associative, 64 entries
L2 Cache                                  None
Trace L1 Cache                            12 KµOPs, 8-way set associative
                                          
Processor Features                        
Floating-point Unit on chip (FPU)         Yes
MMX Instructions (MMX)                    Yes
MMX Instruction Extensions (MMX+)         No
3DNow! Instructions                       No
3DNow! Instruction Extensions (3DNow!+)   No
Streaming SIMD Extensions (SSE)           Yes
Streaming SIMD Extensions 2 (SSE2)        Yes
Multiprocessor Capable                    No
x86-64 Long Mode (LM)                     Yes
Virtual Mode Extension (VME)              Yes
Debugging Extension (DE)                  Yes
Page Size Extension (PSE)                 Yes
Time Stamp Counter (TSC)                  Yes
Model Specific Registers (MSR)            Yes
Physical Address Extension (PAE)          Yes
Machine Check Exception (MCE)             Yes
CMPXCHG8 Instruction (CX8)                Yes
On-chip APIC Hardware (APIC)              Yes
Fast System Call (SEP)                    Yes
Memory Type Range Registers (MTRR)        Yes
Page Global Enable (PGE)                  Yes
Machine Check Architecture (MCA)          Yes
Conditional Move Instruction (CMOV)       Yes
Page Attribute Table (PAT)                Yes
36-bit Page Size Extension (PSE36)        Yes
96-bit Processor Number (PSN)             No
CLFLUSH Instruction (CLFSH)               Yes
Debug Trace Store (DTS)                   Yes
ACPI Supported (ACPI)                     Yes
Fast Save and Restore (FXSR)              Yes
Self Snoop (SS)                           Yes
Thermal Monitor Supported (TM)            Yes
IA-64 Processor Capable (IA-64)           No